1. Technical Field
The technical field relates to an imaging apparatus that can perform a continuous shooting operation, and particularly to the imaging apparatus capable of automatically controlling an interval of the continuous shooting operation.
2. Related Art
A digital still camera that can record still images converts an optical image imaged on an imaging device such as a CCD or a CMOS through an optical system into an electric signal and further performs AD-conversion for the electric signal to generate a digital signal. The digital signal is converted from RAW data into YC data, and is subject to a JPEG compressing process so as to be recorded in an external flash memory such as a memory card.
Recently, digital still cameras that can perform high-speed continuous shooting at an interval of a several shots to several dozens shots per second have come to the market. Such digital still cameras have various functions. These functions enable continuous shooting of people who enjoy sports, moving animals, cars and airplanes, and enable users to select best shots from a plurality of recorded images continuously shot, and display a plurality of arranged images so as to enable the users to view them.
Regarding the continuous shooting function of imaging apparatuses, there is an imaging apparatus that detects a motion of a subject from an image and changes an interval for capturing an image in the continuous shooting according to the speed of the motion of the subject (for example, see Japanese patent application publication No. JP2009-060355A).
In a digital still camera that can perform high-speed continuous shooting, the high-speed continuous shooting can be performed generally until capacity of a storage medium (DRAM) is allowed. However, when the storage medium has no free space, a continuous shooting speed is limited to a speed regulated by a speed of writing data from the recording medium to the memory card. Therefore, the high-speed continuous shooting can be performed continuously for only one to several seconds after starting the continuous shooting, and thereafter the continuous shooting speed becomes enormously slow. For this reason, users may occasionally miss the best shots when a subject that moves quickly such as a person playing a sport is continuously shot. Further, there is a digital still camera that has a function with which a user can set a continuous shooting interval (the continuous shooting speed) in advance. However a moving speed of the subject cannot be frequently predicted, and therefore, such digital still camera is difficult to use.
The above problem can be solved to a certain extent by using a recording medium of which writing speed is high, such as a memory card. In this case, however, since a lot of pieces of image data are recorded in the recording medium such as a memory card, a high-capacity recording medium that is comparatively expensive is necessary. Further, users' burden increases for searching for desired images from a lot of pieces of recorded image data after recording images.
JP2008-131572A discloses a technique that saves capacity of a recording medium for recording video signals. According to JP2008-131572A, a motion of a subject is detected from an image, and when a magnitude of the motion is not more than a predetermined threshold, a recording interval is lengthened, while when the magnitude of the motion is more than the threshold, the recording interval is shortened, so that the capacity of a recording medium can be saved.
JP2008-131572A relates to a monitoring camera having a moving image capturing unit and a recording unit, and its object is to control the recording interval in a long term recording so as to save the entire capacity of the recording medium. However, a capturing interval in the continuous shooting function is not controlled. Therefore, JP2008-131572A does not provide a method for solving the above problem relating to the continuous shooting operation.
JP2009-060355 discloses a technique that can save a capacity of a film medium in a film camera having a film auto-feeding unit. In JP2009-060355A, a sensor for image processing is provided in addition to an imaging unit for film, a motion of a subject is detected by an image process of the sensor, and the capturing interval for continuous shooting is controlled according to the detected motion so that capacity of a film medium can be saved.
However, in the configuration to detect the motion of a subject from a captured image like JP2009-060355A, the motion can be detected only after the image is captured, thereby arising a problem of a response. In an image such as a night view from which the motion is hard to be recognized, the motion cannot be accurately detected. That is to say, JP2009-060355A has a problem in achieving quick and accurate control of the capturing interval at the continuous shooting.
At the continuous shooting, user's camerawork (actual camera motion) is one of important elements for capturing a preferable image. JP2009-060355A detects a motion of a subject in an image and does not detect an actual motion of the camera, and thus the user's camera work (panning) is not taken into consideration, thereby arising a problem in capturing a preferable image according to the motion of a subject.